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Jan 2005

Volume 76, Issue 1, Articles (01xxxx)

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Use of a Joule–Thomson micro-refrigerator to cool a radio-frequency coil for magnetic resonance microscopy

A. C. Wright, H. K. Song, D. M. Elliott, and F. W. Wehrli

Rev. Sci. Instrum. 76, 014301 (2005); http://dx.doi.org/10.1063/1.1824340 (7 pages) | Cited 3 times

Online Publication Date: 17 December 2004

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A method is described for cryogenically cooling a rf detector coil, as used in high-resolution magnetic resonance imaging (MRI), to enhance image signal-to-noise ratio (SNR). By incorporating the rf coil into a Joule–Thomson micro-refrigerator, the coil is precision-cooled to 70 K using only a source of high-pressure nitrogen gas at room temperature, avoiding the need for liquid cryogens. The rf coil is insulated by a glass vacuum dewar that permits its use in proximity to biological tissues. Design and operation of the cryogenic system are described and its performance is demonstrated in a 1.5 T clinical MRI scanner with images of a water phantom and a sheep intervertebral disc specimen. SNR gains of two to three times were obtained, compared to a similar coil at room temperature. The potential of this technology for local high-resolution MRI is discussed.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
87.61.Ff Instrumentation

A microchannel solution mixer for studying microsecond protein folding reactions

Osman Bilsel, Can Kayatekin, Louise A. Wallace, and C. Robert Matthews

Rev. Sci. Instrum. 76, 014302 (2005); http://dx.doi.org/10.1063/1.1834698 (7 pages) | Cited 12 times

Online Publication Date: 22 December 2004

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Many proteins fold through intermediates that are populated in the submillisecond time regime. To monitor directly the formation of these kinetic intermediates, we have developed a simple, robust, easy to assemble continuous flow mixer for studying folding reactions in the 35–1000 μs time regime. The mixer is constructed by laser-machining 75-μm channels in a 127-μm-thick polyimide or polyetheretherketone polymer wafer. Mixing times of ∼ 25 to  ∼ 50 μs can be achieved for a 1/10 dilution reaction of 8 M urea with flow rates of 10–20 mL/min. CCD-based steady-state and time-correlated single-photon-counting-based fluorescence detection strategies are described. Preliminary results on the early events in the refolding of cytochrome c are presented.
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82.39.-k Chemical kinetics in biological systems
87.14.E- Proteins
87.15.Cc Folding: thermodynamics, statistical mechanics, models, and pathways
07.10.Cm Micromechanical devices and systems
47.85.Np Fluidics
36.20.Hb Configuration (bonds, dimensions)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Detection of magnetically enhanced cancer tumors using SQUID magnetometry: A feasibility study

G. G. Kenning, R. Rodriguez, V. S. Zotev, A. Moslemi, S. Wilson, L. Hawel, C. Byus, and J. S. Kovach

Rev. Sci. Instrum. 76, 014303 (2005); http://dx.doi.org/10.1063/1.1834696 (9 pages) | Cited 5 times

Online Publication Date: 22 December 2004

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Nanoparticles bound to various biological molecules and pharmacological agents can be administered systemically, to humans without apparent toxicity. This opens an era in the targeting of specific tissues and disease processes for noninvasive imaging and treatment. An important class of particles used predominantly for magnetic resonance imaging is based on iron-oxide ferrites. We performed computer simulations using experimentally determined values for concentrations of superparamagnetic particles achievable in specific tissues of the mouse in vivo and concentrations of particles linked to monoclonal antibodies specific to antigens of two human cancer cell lines in vitro. An instrument to target distance of 12 cm, into the body, was selected as relevant to our goal of developing a rapid inexpensive method of scanning the body for occult disease. The simulations demonstrate the potential feasibility of superconducting quantum interference device magnetometry to detect induced magnetic fields in focal concentrations of superparamagnetic particles targeted, in vivo, to sites of disease.
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87.19.X- Diseases
85.25.Dq Superconducting quantum interference devices (SQUIDs)
75.50.Tt Fine-particle systems; nanocrystalline materials
07.55.Ge Magnetometers for magnetic field measurements
87.61.-c Magnetic resonance imaging
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